1,3-Dihalo-5,5-dialkylhydantoins, especially 1,3-dibromo-5,5-dimethylhydantoin, 1,3-dichloro-5,5-dimethylhydantoin, 1-bromo-3-chloro-5,5-dimethylhydantoin, and 1-chloro-3-bromo-5,5-dimethylhydantoin, or mixtures of two or more of them, are biocidal agents for use in water treatment. These compounds are, in general, sparingly soluble in water.
Over the years considerable effort has been devoted to the search for improved methods for producing N-halogenated hydantoins. In U.S. Pat. No. 2,971,960 N-brominated compounds such as N-brominated 5,5-di-lower-alkyl hydantoins are formed by treating the alkylhydantoin with bromine in an acidic aqueous solution containing hypochlorite, preferably at a pH between 1 and 4. However, the method of choice has been halogenation of the alkylhydantoin in a basic aqueous medium. Almost invariably the halogen has been introduced into, or formed in situ in, the aqueous medium containing the alkylhydantoin. See in this connection U.S. Pat. Nos. 2,398,598; 2,779,764; 2,868,787; 2,920,997; 2,971,959; 3,121,715; 3,147,259; 4,532,330; 4,560,766; 4,654,424; 4,677,130; 4,745,189; WO 97/43264, published 20 Nov. 1997; Orazi and Meseri, Anales Assoc. Quim. Argentina, 1949, 37, 192-196; Orazi and Meseri, Anales Assoc. Quim. Argentina, 1950, 38, 5-11; Corral and Orazi, J. Org. Chem., 1963, 23, 1100-1104; Jolles, Bromine and its Compounds, Ernest Benn, London, 1966, p. 365; and Markish and Arrad, Ind. Eng. Chem. Res., 1995, 34, 2125-2127.
Shortcomings of prior processes for the N-halogenation of hydantoins include the requirement for careful temperature control (particularly in order to avoid sudden exotherms), long reaction times, foaming due to evolution of gases from decomposition of reactants and/or reaction products, and products of inconsistent quality.
It would be of considerable advantage if a new way could be found of producing N-halogenated hydantoins while avoiding or at least minimizing the extent of the shortcomings referred to above.
Another advantage would be the provision of process technology which enables production in a single halogenation step or operation of “tailor-made” mixtures of 1,3-dihalo-5,5-dialkylhydantoins (preferably 1,3-dihalo-5,5-dimethylhydantoins) even if such mixtures are not always of larger average particle size. By “tailor-made” mixtures is meant that through control or regulation of the halogenation process, it is possible to produce a reaction product containing a mixture of 1,3-dibromo-5,5-dialkylhydantoin together with N,N′-bromochloro-5,5-dialkylhydantoin(s) and optionally 1,3-dichloro-5,5-dialkylhydantoin in which proportions of these halogenated products in the mixture can be controlled so as to be within predetermined experimental limits. Some of these mixtures are new, and are useful as cost-effective biocides especially for water treatment applications.
This invention is deemed to fulfill these objectives in a most effective and efficient manner.